Supramolecular structures formed by the self assembly of ionic fullerenes in binary liquid mixtures
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The self assembly of C60-N, N⬘-dimethylpyrrolidinium iodide (C60-DMePyI) in binary liquid mixtures has been investigated. C60-DMePyI self-organized into nanosheets in a mixture of toluene and iodomethane, and aggregated to form nanofibers in toluene. The dimensions of the nanosheets were several micrometers in length and about 100 nm in thickness. Scanning electron microscope observations indicated that a large number of nanorods having a diameter of about 20-nm formed matted nanosheets. When iodomethane alone was used as a solvent, supramolecular structures such as nanofibers and nanosheets were not produced. Structural analyses of the C60-DMePyI aggregates were carried out by laser Raman spectroscopy and x-ray diffraction (XRD). The Raman spectroscopic results suggested that an ordered chain of successive polyiodine units was formed in all the supramolecular aggregates. The XRD studies showed that the crystal systems of the nanosheets and nanofibers were monoclinic, though with different unit cells.
I. INTRODUCTION
The ordering and organization of nanostructures across lengths of several nanometers by a self-assembly process is a key challenge in the design of advanced materials. In an attempt to meet this challenge, the self assembly of fullerenes or fullerene derivatives has attracted much attention for the past decade. Fullerenes, with their highly hydrophobic carbon cages, are known to self-assemble into nanometer-sized clusters in single solvents and in solvent mixtures. 1–6 Several C 60 containing polymers also aggregate in polar solvents.7–12 Such self-assembled C60 aggregates exhibit various photochemical features. The construction of supramolecular architectures using fullerene derivatives has also been designed for performing specific functions. Miyazawa has reported the formation of certain kinds of nanowhiskers and nanotubes using C60, C70, or C60 derivatives by the liquid/ liquid interfacial precipitation method. 13–15 Onedimensional nanotubules have been built up by the self organization of phthalocyanine-linked fullerene.16 There has been considerable interest in the design and synthesis of two-dimensional nanonetworks using fullerene derivatives, held together by reversible interactions such as hydrogen bonds, metal-ligand interactions, and van der
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0405 J. Mater. Res., Vol. 22, No. 11, Nov 2007
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Waals forces.17–19 Thus, one of the most interesting directions in current fullerene research involves selfassembling behavior.20 Ionic fullerenes also self assemble and exhibit supramolecular nanostructures in solution, on surfaces, and at interfaces21: according to Mannsberger et al.,22 8-(Nmethyl-fulleropyrrolidium-1-yl-chloride)-3,6-dioxanooctan1-ammonium chloride can self organize into a variety of species (vesicles, dendrites, and nanorods); spherical bilayer vesicles of fullerene-based surfactants were prepared in water by Zhou and co-worker
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